Conventionally, a computer mouse comprises a bottom casing and a top cover mounted to the bottom casing, defining an interior space therebetween for accommodating a circuit board. The circuit board is fixed to the bottom casing and comprises a tracking module substantially aligned with an opening defined in the bottom casing. The tracking module comprises a track ball rotatably mounted inside the mouse and partially projects beyond the bottom casing for engaging a fixture surface on which the mouse is moved. The track ball is rotated when the mouse moves on the fixture surface. The rotation of the track ball is converted into electrical signal that is transmitted through an electrical cable soldered to the circuit board to a host computer.
Since the conventional mouse is electrically connected to the host computer by an electrical cable that is soldered to the circuit board of the mouse, a portion of the interior space of the mouse must be occupied by the cable. In addition, the cable that connects the mouse to the host computer imposes limitation to the movement of the mouse on the fixture surface. Thus, an operator is not allowed to completely freely move the mouse to obtain the best operability thereof. Further, dusts may get into the mouse by the rotation of the track ball. This may induce poor engagement between components of the mouse in generating and transmission of the signal indicating the movement of the mouse.
An optic mouse overcomes at least the dust problem by generating the movement signal of the mouse by means of detection of reflection light. The optic mouse comprises a bottom casing and a top cover attached to the bottom casing with a circuit board fixed between the casing and the cover. An illuminating element, such as a light emitting diode (LED), is mounted to the circuit board for projecting a light beam through an opening defined in the bottom casing. The light beam is reflected by a fixture surface on which the mouse is moved. The reflected beam transmits through the opening of the casing and detected by a sensor substantially aligned with the opening. A set of optical elements, including lenses, is arranged between the circuit board and bottom casing for directing and transmitting the light beam from the illuminating element to the sensor.
The conventional optical mouse, however, suffers non-uniform projection of light from the illuminating element, which is generally an LED. As shown in FIG. 1 of the attached drawings, the LED comprises a chip 1 having a light projection surface from which the light beam is projected. A solder pad 2 is formed on a central portion of the light projection surface for connection with electrical conductors through which electricity is transmitted to the LED. The solder pad 2, due to being located on a central portion of the light projection surface, blocks a substantially amount of light projected from the light projection surface, forming a dark zone, whereby light projected out of the mouse is not uniform. Such a non-uniform light beam, after being reflected by the fixture surface, induces a poor detection signal on the sensor.